Electronic discharge device



.Sept 25, MSH E. DONA-IH ELECTRONIC DISCHARGE DEVICE Filed July 24, 1948 I N VEN TOR m w//v D0/VA 7h f. fw M A ef/v r Patented Sept. 25, 1951 UNITED STATES PATENT OFFICE 9 Claims. (Cl. 313-325) The present invention relates to electronic discharge devices and, more particularly, to electronic discharge devices or tubes of the type comprising a spark gap within an envelope which latter is provided with a window (generally a thin metal foil) through which electrons set in motion by the voltage difference across the spark gap may be discharged intothe atmosphere. Tubes of this description are well known and are used for the purpose of sterilizing or otherwise treating matter by electron bombardment.

In tubes of the type set forth above, each discharge is preceded by a very high surge voltage (e. g. of the order of several million volts) built up across the spark gap which voltage must be sustained by the insulating material supporting the electrodes of the gap in spaced-apart relationship; these electrodes are generally a grounded metal foil, representing the aforesaid window, and a cathode, both supported directly from the tube envelope. found that in such tubes special precautions must be taken lest, even where the dielectric strength of the envelope material is theoretically suicient to withstand the voltages employed, breakdown occur as the result of parasitic charges and non-uniform field distribution. None of the tubes heretofore designed has proved fully satisfactory in this respect, as far as I am aware.

It is, therefore, an object of the present invention to provide an improved electronic discharge device of the character described.

It is another object of my invention to provide, in an electronic discharge device comprising a preferably tubular envelope of insulating material and a pair of electrodes supported by said envelope in spaced-apart relationship, means for insuring a substantially uniform field distribution along the envelope and for dissipating parasitic charges collected thereon, whereby the life span of the device will be increased.

A further object of this invention is to provide, in an electronic discharge tube having a spark gap suitable for electron bombardment of matter preferably located outside the tube envelope, means for directing the electrons upon a predetermined path while substantially preventing them from reaching any part of the envelope intermediate the electrodes of the gap.

Still another object of the invention is to provide a method of making a tube envelope in such manner that the preceding objects will be realized.

The above and other objects of the invention will become apparent from the following description, reference being had to the accompanying drawing in which:

Fig. 1 is a longitudinal cross section of a well known electron tube of the characterdescribed, this ligure also illustrating schematically the improvement proposed in accordance with the present invention;

Figs. 2- and 3 are elevations, partly in section, of two embodiments of tubes in accordance with the invention;

Fig. 4 is a complete circuit diagram of an arrangement for producing large and intermittent electronic discharges, utilizing a tube according to the invention; and

Fig. 5 shows a fragmentary modification of` the circuit of Fig. 4.

Fig. l shows an electron discharge device Ill comprising a tubular envelope I I, e. g. of ceramic material, from the top of which a cathode I2 is suspended by a conductor I3. The other electrode of the spark gap is formed by a metal foil I4 inserted in the bottom of the envelope II. The foil I4 is grounded as shown at I5, and a voltage V is intermittently applied across the electrodes I2,Y I4, resulting in a violent discharge of electrons from the cathode I2 which penetrate the window I4 as indicated by the arrow I6. Since the cathode I2 is unheated, the electrons necessary for the discharge are obtained through ionization within the tube which contains air or gas at low pressure.

It has been believed for some time that the reason for the failure of a tube of the type shown in Fig. 1, if subjected to high voltages, lies in the fact that the distribution of voltages along the internal and the external surfaces of the envelope I I is not uniform, thus giving rise to voltage differences across the walls of the tube which exceed the breakdown strength of the dielectric material, resulting in the destruction of the envelope. Accordingly, such tubes have been l provided with spaced conducting members Il, of

' l were it not for the fact that each ring during discharges will act as an auxiliary anode, thereby attracting electrons which will alter the potential of the ring as determined by its position within the capacitive voltage divider; this is especially true for the lower rings whose capacity to ground is large. Accordingly, a non-uniform field will again exist and will again place undue stresses upon the dielectric material of the envelope.

Furthermore, the drain upon the electron stream caused by the rings I1 will materially reduce the output of electrons passing through the window I4 whereby the efficiency of the tube will be impaired. Finally, the composition of the tube I of annular portions of insulating material alternating with the rings I1 entails a mechanical weakening of the structure as compared with a tube wherein the envelope consists of a unitary piece of insulating material.

As will be subsequently apparent from the description of Fig. 4, the voltage across the electrodes I2, I4 remains substantially zero during the major part of the interval between discharges, then rises steeply to its peak, and immediately thereafter drops to substantially zero as the tube discharges.

VAccording to the present invention, I propose to overcome the first of the above-mentioned drawbacks by galvanically interconnecting the electrodes I2, I4 over an inductive circuit which includes the auxiliary conductors I1, and which, in a simple form of the invention, may include a set of series-connected induction coils or chokes I8 as shown in Fig. 1, each auxiliary conductor or ring I1 being connected to the junction of two coils I8. y The coils I8 present a substantially infinite impedance to the steep anks of the voltage pulses preceding the discharges, yet in the interval between discharges facilitate the dissipation of stray charges built up on the rings as well as on the dielectric adjacent thereto. During each voltage peak, therefore, the rings I'I will act as a capacitive voltage divider producing an essentially uniform electric field inside and outside the tube envelope, and undue electric stresses upon the dielectric material will be avoided.

Even more advantageous is the tube Ilia of Fig. 2. Here the annular members I1 have been replaced by an auxiliary conductor Ila of helical configuration which penetrates the tube envelope IIa. It will be appreciated that the inductivity of auxiliary conductor I'Ia will be of the same order as the combined inductivity of the serially connected coils I8 in Fig. l. The helical conductor Ila terminates at the top in a. disk-like member I9, establishing conductive contact with the cathode I2, and galvanically contacts at the bottom the foil I4. The foil I4 is again grounded as schematically indicated at I 5.

The helical member I'Ia becomes the source of a magnetic field, on being subjected to the surge voltages, which field extends in the axial direction of the tube. Such a magnetic field will have a focusing effect upon the electrons emitted from the cathode I2, that is to say it will tend to prevent any' electron from reaching the conductor IIa. Thus, with suitable dimensioning of this conductor in relation to the wave form of the surge voltage, it will be possible to direct most if not all electrons upon the window or foil I4, either concentrating them upon a predetermined spot thereof (such as the center) or, as will be preferable in some instances, sufliciently defocusing them'to have them emerge at widely spaced points of the foil.

The focusing effect of a magnetic eld upon an electron having a velocity component transverse to the ileld, as is well known, consists in the tendency of the field to force the electron into a helical path whose axis extends in the direction oi' the eld and whose diameter is determined by the magnetic field strength and by the magnitude of the said component. If we assume that the electron undergoes constant radial acceleration as the result of the existence of an auxiliary conductor such as I'I or I'Ia, the path of the electron will still be helical but the helix will lie on the periphery of a cone rather than a cylinder. Accordingly, Fig. 3 shows a further tube according to the invention, indicated at Illb, which is of frusto-conical configuration; thereby the likelihood of any electron impinging upon the auxiliary conductor or conductors will be still further reduced.

From Fig. 2 it will be seen that the envelope Ila of tube lila no longer consists of discrete portions of insulating material as is true of tube I0 in Fig. l, but is made in a single piece of di' electric material of helical configuration, which may be directly moulded or cast between the threads of the conductive member Ila. Fig. 3 shows how even greater mechanical strength may be obtained without sacrificing any of the advantages of the invention. According to Fig. 3, the envelope IIb is a single, generally tubular (in the present case frusto-conical) piece of insulating material carrying a helical conductive strip IIIa on the inside and a similar conductive strip II1l on the outside. The two strips extend opposite one another along the inner and outer surface. respectively, of the envelope vIIb and are conductively connected to the cathode I2 by means of an lrmer and an outer layer Isa, I9b of conductor material; they are also in .contact with the foil I4. Strips I I'Ia, IIIb may be thin layers of metal applied to the envelope IIb in any suitable manner, as by spraying.

According to still another feature of the invention, the auxiliary conductor such as Ila or I Ila, IIIb may be utilized as a carrier for a magnetic biasing current which may serve for the focusing or defocusing of the electrons in the manner previously set forth. Referring to Fig. 4, there is shown a surge voltage generator 20 of a type well known per se, which may be advantageously used in combination with a tube according to the invention and indicated schematically at H0. Tube I|0 may be of the type illustrated, for example, in Fig. 2 or 3. The generator 2l comprises a source of direct current shown here schematically as a battery 2|, connected by way of a current-limiting resistor 22 across a series of networks 23a, 23h, 23e each comprising two resistive series arms 24a, 24h, 24c and 25a, 25h, 25e, a capacitive shunt arm 26a, 2Gb, 26e, 26d, and a diagonally arranged spark gap 21a, 2lb, 21e, extending between respective terminals 28a., 29a; 2Gb, 29h; 28e, 29e. Although only three networks or voltage multiplication stages are shown, any suitable number thereof may be used. The high voltage terminal 28d of the last network 23c is connected to ground over a circuit including the auxiliary spark gap 29 in series with the main gap of the tube I I0.

The operation of this arrangement is as follows:

Battery 2|, having a voltage Vo, charges capacitors 26a,V 2Gb, 26e and 26d through resistor 22 untila voltage V1 exists across these capacitors. The spark gap 21a is arranged to break down at this voltage. thereby virtualLv short-circuiting the terminals 28a and 29a and s A adding the voltage existing across condenser 26a to that existing across condenser 2Gb, the impedance of the series arms 24a, 25a being at this instant large relative to that of -the discharged path 26a, 21a. etc. Now a voltage of approximately 2 Vi exists across the gap 21h which in turn breaks down, applying a voltage of 3 V1 to gap 21e. The latter voltage, as will be apparent, is now applied across gap 29 and tube H in series, gap 29 having been provided for the purpose of preventing a breakdown of the main gap at the initial voltage V1 before multiplication sets in. It will be noted that the potential of cathode l2 is caused to rise sharply to a value of n V1 wherein 11. is the number of networks such as 23a.

By shunting the auxiliary gap 29 by a high resistance 30,` it will be possible to energize the auxiliary conductor of tube H0, indicated generally at H1, by a direct current serving to produce the desired magnetic field. Resistor 30 may be adjustable, as shown, in order to permit the focusing effect of the eld to be varied.

In Fig. 5, wherein the resistance 30 has been omitted, the biasing current is derived from an auxiliary source of current shown as a battery Il, the latter being connected in series with a protective choke 32 serving to prevent the passage of surge current through the battery 3l. Although the invention has been described with reference to certain preferred embodiments it is to be understood that the same is not limited to the form speciilcally disclosed herein and that various modications and adaptations may be made without departing from the spirit or exceeding the scope of the invention. In addition to electronic bombardment tubesV as hereinabove referred to, the invention may be employed in connection with any electronic discharge device wherein a voltage of steep wave form results in an electronicv discharge. Such voltages may, of course, be derived from suitable generators such as relaxation oscillators other than the generator shown in Fig. 4, which has been shown merely by way of example and is not claimed per se.

Furthermore, while there have been shown in Figs. 2 and 3 two exemplary embodiments of the invention, it is to be understood that the conductor arrangement of Fig. 3 may also be applied to the cylindrical tube form of Fig. 2. or the conductor arrangement of Fig. 2 may be used in combination with a flared or frusto-conical tube as shown in Fig. 3; many other changes will likewise be obvious to those skilled in the art without inventively distinguishing from the present disclosure.

'I'he invention also contemplates a method of making a tube of the general character shown in Fig. 2. This method consists in winding an insulated conductor, which may be ordinary wire, into a coil having closely adjacent turns. fusing together the insulationv of the adjacent turns, whereby a tube will be formed, and removing suiilcient insulation from the inner and the outer surfaces of said tube to bare the belically wound wire.

What I claim as novel' and desire to secure by Letters Patent is:

'1. An electronic discharge device comprising an envelope oi' insulated material, a pair of electrodes forming a spark gap withinv said envelope. and auxiliary conductor means substantially oo- Number extensively disposed along the inner and outer surfaces of said envelope, said conductor means representing a highly inductive path which galvanically interconnects said two electrodes.

2. An electronic discharge device according to claim 1 wherein said auxiliary conductor means comprise a plurality of substantially parallel rings extending through said envelope and a plurality of serially connected inductances inserted between adjacent ones of said rings and between each of said electrodes and a respective ring ladjacent thereto.

3. An electronic discharge device according to claim 1 wherein said envelope is of tubular configuration, said auxiliary conductor means com-l prising at least one helical conductor connected between said two electrodes and extending coaxially with said envelope.

4. An electronic discharge device comprising a generally tubular envelope oi insulating material,v a pair of electrodes supported from said envelope in spaced-apart relationship so as to form a spark gap within said envelope, and an auxiliary conductor of helical conguration extending coaxiallv with and contiguous to the said envelope, said conductor galvanically interconnecting said two electrodes.

5. An electronic discharge device comprising a generally tubular envelope of insulating material, a cathode extending into said envelope and supported from one end thereof, a foil-like anode inserted into the other end of said envelope so as to permit the passage of electrons from said cathode into the atmosphere, and helical conductor means galvanically interconnecting said anode and said cathode, said conductor means being contiguous with the inner and outer surfaces oi' said envelope at points opposite one another across the wall of the envelope.

6. An electronic discharge device according to claim 5 wherein said envelope is ared outwardly towards said anode. 7. An electronic discharge device according to claim 5 wherein said conductor means comprises a single helical conductor extending through the wall oi said envelope.

8. An electronic discharge device according to claim 5 wherein said conductor means comprise first and second helical conductors extending along the inner and outer surfaces of said envelope. respectively.

9. An electronic discharge device according to claim 5, further comprising a magnetic biasing circuit including said helical conductor means, said biasing circuit also including a source of direct current connected across said anode and cathode.

ERWIN DONATE.

REFERENCES CITED The following references are of record in the ille of this patent:

UNITED STATES PA Y Name Date 2,005,021 Brasch et al. June 18, 1935 2,048,556 McArthur July 21, 1936 2,145,727 Lloyd. Jr. Jan. 31, 1939 2,206,558 Bennett July 2, 1940 2,375,830 Spencer May 15, 1945 2,386,820 Spencer Oct. 16, 1945 2,414,622 Watrous, Jr Jan. 2l, 1947 

